Increase of retroviral infection in vitro by the binding of antiretroviral antibodies

Viral vectors for gene transfer: a review of their use in the treatment of human diseases

The efficient delivery of therapeutic genes and appropriate gene expression are the crucial issues for clinically relevant gene therapy. Viruses are naturally evolved vehicles which efficiently transfer their genes into host cells. This ability made them desirable for engineering virus vector systems for the delivery of therapeutic genes. The viral vectors recently in laboratory and clinical use are based on RNA and DNA viruses processing very different genomic structures and host ranges. Particular viruses have been selected as gene delivery vehicles because of their capacities to carry foreign genes and their ability to efficiently deliver these genes associated with efficient gene expression. These are the major reasons why viral vectors derived from retroviruses, adenovirus, adeno-associated virus, herpesvirus and poxvirus are employed in more than 70% of clinical gene therapy trials worldwide. Among these vector systems, retrovirus vectors represent the most prominent delivery system, since these vectors have high gene transfer efficiency and mediate high expression of therapeutic genes. Members of the DNA virus family such as adenovirus-, adeno-associated virus or herpesvirus have also become attractive for efficient gene delivery as reflected by the fast growing number of clinical trials using these vectors. The first clinical trials were designed to test the feasibility and safety of viral vectors. Numerous viral vector systems have been developed for ex vivo and in vivo applications. More recently, increasing efforts have been made to improve infectivity, viral targeting, cell type specific expression and the duration of expression. These features are essential for higher efficacy and safety of RNA- and DNA-virus vectors. From the beginning of development and utilisation of viral vectors it was apparent that they harbour risks such as toxicities, immunoresponses towards viral antigens or potential viral recombination, which limit their clinical use. However, many achievements have been made in vector safety, the retargeting of virus vectors and improving the expression properties by refining vector design and virus production. This review addresses important issues of the current status of viral vector design and discusses their key features as delivery systems in gene therapy of human inherited and acquired diseases at the level of laboratory developments and of clinical applications.

Retrovirus infection: effect of time and target cell number

Using a model amphotropic recombinant retrovirus encoding the Escherichia coli lacZ gene and quantitative assays to measure virus infection, we have determined the effects of time and target cell number on infectivity. Infection of various numbers of NIH 3T3 fibroblasts showed that the extent of lacZ virus infection was dependent on virus concentration and independent of target cell number. These results demonstrate that multiplicity of infection is not an accurate predictor of the efficiency of retroviral infection. Varying the time of viral infection revealed that maximal infection occurred after greater than 24 h of exposure of the cells to the lacZ virus. Half-maximal infection occurred after 5 h of exposure. After 2 h of adsorption at 37 degrees C, the majority of infectious virus was not adsorbed to cells but was unbound and able to infect other cells. These results are discussed in terms of both their relevance to the fundamental biology of retrovirus infection and the use of recombinant retroviruses for retrovirus-mediated gene transfer with purposes of gene therapy.

Two-phase approach for the expression of high-affinity human anti-human immunodeficiency virus immunoglobulin Fab domains in Escherichia coli

We describe here a two-phase approach for the development of high-affinity human anti-HIV immunoglobulin Fab domains in a bacterial expression system. The first phase of this technique involves the generation of human hybridoma cell lines producing high-affinity antibodies (MAbs). Anti-HIV-1 human MAbs from peripheral blood lymphocytes (PBLs) were prepared from an HIV-1-seropositive patient and from an HIV-1-seronegative volunteer immunized with HIV-1 rgp160. One MAb (T15G1), derived from the blood of the seropositive donor, was specific for HIV-1 gp41, recognized gp41 on the surface of HIV-1-infected cells and bound this antigen with an apparent dissociation constant of 4 x 10(-10) M. A second MAb (M7B5), developed from the immunized volunteer, was specific for HIV-1 gp120 with a dissociation constant on the order of 8 x 10(-10) M, but was unable to recognize cell surface antigen. In the second phase of this technique the Fab domains of these two MAbs were molecularly cloned into a bacterial expression vector. mRNA was isolated from the M7B5 and T15G1 hybridoma cell lines and used as a template for the production of cDNA. The cDNA was amplified using the polymerase chain reaction (PCR) technique, and then fused, in frame, into a bacterial expression vector. The recombinant Fabs (rFabM7B5 and rFabT15G1) were expressed as dicistronic messages in bacteria using the IPTG-inducible lactose promoter (LacZ). DNA sequencing was used to define the gamma chain isotypes and the VH and VL chain gene usage. The binding specificities of rFabM7B5 and rFabT15G1 were indistinguishable from their respective intact MAbs.(ABSTRACT TRUNCATED AT 250 WORDS)

Pathogenesis of human immunodeficiency virus infection

The lentivirus human immunodeficiency virus (HIV) causes AIDS by interacting with a large number of different cells in the body and escaping the host immune response against it. HIV is transmitted primarily through blood and genital fluids and to newborn infants from infected mothers. The steps occurring in infection involve an interaction of HIV not only with the CD4 molecule on cells but also with other cellular receptors recently identified. Virus-cell fusion and HIV entry subsequently take place. Following virus infection, a variety of intracellular mechanisms determine the relative expression of viral regulatory and accessory genes leading to productive or latent infection. With CD4+ lymphocytes, HIV replication can cause syncytium formation and cell death; with other cells, such as macrophages, persistent infection can occur, creating reservoirs for the virus in many cells and tissues. HIV strains are highly heterogeneous, and certain biologic and serologic properties determined by specific genetic sequences can be linked to pathogenic pathways and resistance to the immune response. The host reaction against HIV, through neutralizing antibodies and particularly through strong cellular immune responses, can keep the virus suppressed for many years. Long-term survival appears to involve infection with a relatively low-virulence strain that remains sensitive to the immune response, particularly to control by CD8+ cell antiviral activity. Several therapeutic approaches have been attempted, and others are under investigation. Vaccine development has provided some encouraging results, but the observations indicate the major challenge of preventing infection by HIV. Ongoing research is necessary to find a solution to this devastating worldwide epidemic.

Human immunodeficiency virus infection of monocytes: relationship to Fc-gamma receptors and antibody-dependent viral enhancement

Antibodies that augment human immunodeficiency virus (HIV) infectivity of monocytes through Fc receptor (FcR) type III for IgG have been found in the blood of sero-positive patients and immunized chimpanzees. This study investigated the effect of acute and chronic HIV infection, as well as protein kinase C activators capable of up-regulating latent HIV, on the expression of these receptors. In addition, the frequency of this antibody-dependent enhancement (ADE) phenomenon was estimated using purified IgG from HIV-1 seropositive individuals at various clinical stages of infection. The existence of an FcR-dependent pathway for ADE of HIV-1 infection in peripheral blood monocytes and promonocytic U937 cells was confirmed in sera from a small subset of patients, and the phenomenon extended to FcR types I and II. The level of ADE activity was minimal, however, and no relationship between the presence or magnitude of the ADE phenomenon and clinical stage was uncovered. Finally, perturbations which activate a latent HIV infection were shown to concomitantly up-regulate FcR on infected and uninfected cells. This suggests a positive feedback loop linking up-regulation of latent infection, enhanced expression of low affinity HIV receptors such as FcR, and viral spread.

Failure of a human immunodeficiency virus (HIV) immune globulin to protect chimpanzees against experimental challenge with HIV

To assess the possible efficacy of passive immunization against human immunodeficiency virus (HIV) an immune globulin was prepared from plasma of HIV-seropositive donors selected to be among those having the top 12.5% of virus-neutralizing antibody titers. The immune globulin was treated with pepsin to render it intravenously tolerable. The preparation, which we termed HIVIG, neutralized 100 tissue culture 50% infective doses (TCID50) of HIV at an average dilution of 1:1000 in neutralization tests in vitro. During preparation HIVIG was subjected to virus inactivation and removal procedures that in theory resulted in a reduction in HIV infectivity by a factor of 10(25). At a dose of 9-10 ml/kg of body weight both the virus-inactivated source plasma and the final immunoglobulin preparation were noninfective and without adverse effect in two chimpanzees. Two chimpanzees inoculated intravenously with HIVIG at 1 ml/kg and two inoculated with 10 ml/kg were challenged intravenously 1 day later with 400 TCID50 of the same strain of HIV (HTLV-IIIb) used in neutralization assays in vitro. All animals became infected. Incubation periods to virus isolation (by cocultivation with human mononuclear cells) in HIVIG recipients did not differ significantly from the incubation period seen in a control animal that received a normal anti-HIV-free immunoglobulin. These findings may have implications for understanding the failure of experimental vaccines to protect against HIV challenge in chimpanzee experiments.

Antibody-mediated activation of Sindbis virus

The biological activity of an anti-Sindbis monoclonal antibody (MCAB 49) has been explored. The antibody recognizes an epitope on the E2 glycoprotein of Sindbis virus and, in the presence of complement (C'), neutralizes virus infectivity. In the absence of C', reaction of the antibody with our laboratory strain of Sindbis, SB, increased the number of plaque-forming units (PFU) detected on baby hamster kidney (BHK) cells rather than neutralizing virus infectivity. The elevated titers of SB approached, but never exceeded, the number of virions calculated from the particle:PFU ratio, indicating that the additional PFU might have resulted from activation of normally noninfectious particles. The apparent activation could not be attributed to disaggregation of SB by MCAB 49 as shown by ultraviolet inactivation experiments with antibody-treated and untreated virus preparations. Fc receptors did not appear to be involved in the antibody-mediated activation. Fab' and F(ab')2 fragments of MCAB 49 also increased the number of observed PFU of SB. Control monoclonal antibodies of the same isotype, but specific for the tobacco etch virus capsid protein, were unable to compete for cellular binding sites with the SB/MCAB 49 complex. Rather, the SB/MCAB 49 complex appeared to utilize the same receptor(s) as SB in that SB and the SB/MCAB 49 complexes competed with each other for binding sites on BHK cells. Binding studies with 32P-labeled SB showed that a higher proportion of MCAB 49 activated virions than untreated virions associated with BHK cells. Moreover, activated virions were much less susceptible to elution. These results suggest that reaction which MCAB 49 may facilitate successful attachment of SB to its receptor, or receptors, on BHK cells.

Antibody-dependent enhancement of human immunodeficiency virus type 1 infection

Two components of human serum enhance human immunodeficiency virus type 1 (HIV-1) infection and mask HIV-1 neutralising antibody activity. The first is heat-stable, unique to HIV-1 seropositive sera, and is removed by protein-A chromatography. The second is heat-labile and ubiquitous; it is found in normal serum and is removed by heating at 60 degrees C for 1 h or by treatment with cobra venom anticomplementary protein. Additionally, complement component C3 deficient serum lacks the labile activity although Clq deficient serum contains the labile factor. The data suggest that the two components are antibody and the alternative pathway of complement fixation. The mechanism of action does not involve an increase in either complement-mediated cytolysis or syncytium formation. The activity has been identified in 11 of 16 patients tested to date.

Antibody-mediated binding of a murine ecotropic Moloney retroviral vector to human cells allows internalization but not the establishment of the proviral state

We have attempted to introduce a neomycin-resistance gene, recombined in a murine (ecotropic) Moloney retrovirus, into HEp2 human cells which are resistant to infection by this retrovirus. To allow the binding of the retroviral vector on HEp2 cells, we have tested several antibody constructions between two monoclonal antibodies, one (mAb 5E9) directed against the human transferrin receptor and the other (mAb 615) directed against the gp70 envelope viral protein. The crosslinking of mAbs 5E9 and 615 by a sheep anti-murine kappa light chain antibody allowed the binding of virus on HEp2 cells. After incubation at 37 degrees, virus was internalized by HEp2 cells. However, no neomycin-resistant colonies of HEp2 cells have been obtained under various conditions. Our results suggest that binding and internalization of a retrovirus are not sufficient for establishment of the proviral state in cells which do not express a specific receptor.

New approaches to animal vaccines utilizing genetic engineering

Control of infectious diseases in livestock is an important determinant in the success of a nation's effort to efficiently meet its need for animal products. Genetic engineering offers many new options in the design of animal vaccines. Monoclonal antibodies, DNA cloning, recombination, and transfection are examples of techniques that facilitate innovative strategies in antigen identification, production, and delivery. This article reviews the use of genetic engineering in the production of vaccines directed against foot-and-mouth disease virus and other important pathogens of animals. The advantages and disadvantages of vaccines produced through the use of genetic engineering are discussed.

A human immunodeficiency virus type 1 (HIV-1) infection-enhancing factor in seropositive sera

While testing sera for Human Immunodeficiency Virus neutralizing antibody titers, three sera were identified which had the ability to enhance infectivity of the virus. The sera were from three different individuals residing in Nashville, TN. The enhancing factor was not removed by either filtration through 0.05 micron filters or by incubation for one hour with a stoichiometric amount of protein A sepharose. Two of the sera were able to enhance infection by two divergent isolates (HTLV-IIIB and HTLV-IIIRF) while one was only capable of enhancing infection of target cells by HTLV-IIIB. None of the sera induced syncytium formation in chronic HIV-infected cells. The findings suggest that the substance is neither a virus nor an IgG class 1 or 2.